Thanks to Kit Baum, a new package -bpmedian- is now available for download from SSC. In Stata, use the -ssc- command to do this.
The -bpmedian- package is as described as below on my website. It contains two modules, -bpmedian- and -bpdifmed-. The -bpmedian- command estimates a median, using the Bonett-Price standard error, and stores the results as estimation results. The -bpdifmed- command computes Bonett-Price confidence intervals for two medians and their difference (or ratio). References for the Bonett-Price method are given in the on-line help.
Note that, in general, the difference between two medians (as estimated by -bpdifmed-) is not the same parameter as the Hodges-Lehmann median difference estimated by -cendif- (part of the SSC package -somersd-) and by Duolao Wang's package -npshift- (distributed by the old Stata Technical Bullletin and accessible using -findit-). However, the two parameters are the same when the two subpopulation distributions being compared either are symmetrical or differ only in location.
Best wishes
Roger
Roger B Newson BSc MSc DPhil
Lecturer in Medical Statistics
Respiratory Epidemiology and Public Health Group
National Heart and Lung Institute
Imperial College London
Royal Brompton Campus
Room 33, Emmanuel Kaye Building
1B Manresa Road
London SW3 6LR
UNITED KINGDOM
Tel: +44 (0)20 7352 8121 ext 3381
Fax: +44 (0)20 7351 8322
Email: [email protected]
Web page: http://www.imperial.ac.uk/nhli/r.newson/
Departmental Web page:
http://www1.imperial.ac.uk/medicine/about/divisions/nhli/respiration/popgenetics/reph/
Opinions expressed are those of the author, not of the institution.
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package bpmedian from http://www.imperial.ac.uk/nhli/r.newson/stata10
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TITLE
bpmedian: Bonett-Price confidence intervals for medians and their contrasts
DESCRIPTION/AUTHOR(S)
bpmedian calculates a Bonett-Price confidence interval for a median,
using the Bonett-Price standard error, and saves the results as
estimation results. These can then be saved in an output dataset (or
resultsset), using the parmest package (downloadable from SSC), and
then input to the metaparm module of the parmest package to calculate
Bonett-Price confidence intervals for a linear contrast between
medians of independent groups. bpdifmed calculates Bonett-Price
confidence intervals for the medians of two groups, defined by a
grouping variable, and also for their difference or ratio.
Author: Roger Newson
Distribution-Date: 27may2009
Stata-Version: 10
INSTALLATION FILES (click here to install)
bpmedian.ado
bpdifmed.ado
bpmedian.sthlp
bpdifmed.sthlp
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